The precipitated silicas that are used are highly dispersible. They have relatively high surface areas which many patent claims go up to 400m2/g. They have surface moisture which has to help react with the silanes but which also is driven off during the process steps. Any residue water and free ethanol can cause processing problems during the tire manufacturing steps. In combination with the coupling agents the water and the silanol groups on the silica surface react with the silane during mixing to give a silica surface which has the potential of reacting via the sulfur groups to react with the rubber double bonds during the vulcanization stage. The combination of coupling agent and filler gives viscoelastic properties that improve the tire performance. Some of the commercial products we’ve seen are Zeosil-Rhodia, Ultrasil-Degussa, Hi-Sil-PPG, and Zeopol-Huber.